Project Summary/Abstract This proposal combines my two NIGMS grants. Our work on the M2 proton channel from influenza A virus (GM56423) currently focuses on the mechanism of proton movement through the channel. M2 is also the target of the amantadine class of influenza drugs, and most isolates of influenza A virus are now amantadine- resistant. Crystallographic structures of M2 in various functional states will be solved at very high resolution using the X-ray free electron laser to enable structure determination at room temperature. Parallel, collaborative studies use single-molecule measurement and 2DIR to probe dynamics. Very high-resolution structures of a series of small molecule inhibitors in complex with amantadine-resistant mutants of M2 are being determined, to enable our collaborators to conduct structure-based drug design. De novo protein design (GM54616) provides a means to test and refine our understanding of protein structure and function. We address questions of sequence-specific recognition in membranes. A variety of methods exist for the design or selection of antibodies and other reagents that recognize the water-soluble regions of proteins. However, companion methods for targeting Transmembrane (TM) regions are not generally available. Therefore, we are developing methods for the computational design of peptides that target TM helices in a sequence-specific manner, focusing on EGF receptors (collaboration with Natalia Jura) and integrins (collaboration with A. Orr). To elucidate the mechanisms by which proton-coupled transporters function, we have designed model proteins that use proton gradients to drive transport of transition metal ions up a gradient. We are increasing the efficiency of these minimal models and also expanding our methods to allow design of phosphate transporters and lipid flippases. We propose to continue work on the design of model diiron proteins to determine how a protein tunes the properties of these cofactors to affect diverse O2- dependent processes such as substrate oxidation and radical formation. We are designing water and membrane-soluble versions of the protein; by varying the identity and geometry of ligands and the water- accessibility of the center to determine how these parameters they define reactivity. We are studying the mechanisms by which bacterial histidine kinases transmit conformational information through multi-domain TM proteins. HKs are widely used by bacteria to sense and respond to diverse environmental cues such as nutrients or noxious substances. Crystal structures of various truncated domains of HKs have been solved. However, there are no high-resolution structures for HK membrane- spanning domains or full-length HKs, and their signaling mechanism is a matter of debate. By integrating structural information from diverse experimental techniques and functional measurements of HKs we seek to elucidate the mechanism of signaling in HKs. 59